The human brain generates electric signals. These signals are very weak, but can be measured non-invasively by various methods. One of such method is the biomagnetism-measuring method which is used to measure the magnetic field on the outer surface of the head created by electric currents in the brain.
A magnetoencephalography (MEG) system (hereinafter referred to as the MEG system) is a specially improved, highly sensitive device for detecting magnetic fields, and comprises magnetic field sensors, detectors for the currents flowing through the sensors, and related electronic units. The MEG system has much potential as a non-invasive device for measuring brain functions because it has high time and space resolutions.
The magnetic field sensors of a planar type used in such a system typically comprise electric wires in the shape of multi-loop coils that create minute electric currents when they are penetrated by a magnetic flux. For example, as shown in FIG. 3, a sensor comprises a coil (a) for the magnetometer, and two directional derivative coils (b) and (c) for the gradiometer that detects the direction of magnetic field gradient. These three coils, (a), (b), and (c), are combined, overlaid, and integrated with each other to obtain a multi-layer laminate. Sensors, without coil (a) but comprising the coils (b) and (c) are in common use. Also, sensors using only the coil (a) are also available.
Each sensor coil is required to have a surface area of a few square centimeters for the coil to have enough sensitivity in the above-described system. If sensor coils requiring such an area were arrayed closely on the surface of the head, the number of coils would have to be limited, as shown in FIG. 2, with the upper limit being several hundreds of channels at the largest.
One objective of this invention is to create a super-multichannel MEG system capable of very high resolutions ranging from several hundreds to several tens of thousands of magnifications, with said system comprising sensors characterized by the sensor coils being printed on thin films in positions shifted from each other laterally and longitudinally by a length of {a}/{n} and the sensor coils being laminated in a number of {n}2 sheets where {a} is the length of a side of the thin-film coil, and {n} is a natural number, and wherein the signals coming from many corresponding thin-film sensors are sent in parallel with each other, and are switched over by the input unit of each multichannel-Superconducting QUantum Interference Device (SQUID).
Another objective of this invention is to create a super-multichannel MEG system capable of very high resolutions wherein the sensors are produced as described above by printing sensor coils on thin films in positions shifted from each other laterally and longitudinally by a length of a/n and laminating {n}2 sheets of thin-film coils, and wherein a multiple number of such sensors are arrayed longitudinally and end-to-end, while aligning them accurately, to make it possible to detect the difference in electric currents generated by the corresponding coils and to measure the primary derivative or the high-order derivative in the axial direction of the magnetic field.